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TBEL is a powerful expression language for ThingsBoard platform user-defined functions. Original implementation is based on MVEL.

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/**
 * MVEL 2.0
 * Copyright (C) 2007 The Codehaus
 * Mike Brock, Dhanji Prasanna, John Graham, Mark Proctor
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.mvel2.integration.impl;

import org.mvel2.integration.VariableResolver;

import static org.mvel2.DataConversion.canConvert;
import static org.mvel2.DataConversion.convert;

public class SimpleSTValueResolver implements VariableResolver {
  private Object value;
  private Class type;
  private boolean updated = false;

  public SimpleSTValueResolver(Object value, Class type) {
    this.value = handleTypeCoercion(type, value);
    this.type = type;
  }

  public SimpleSTValueResolver(Object value, Class type, boolean updated) {
    this.value = handleTypeCoercion(type, value);
    this.type = type;
    this.updated = updated;
  }

  public String getName() {
    return null;
  }

  public Class getType() {
    return type;
  }

  public void setStaticType(Class type) {
    this.type = type;
  }

  public int getFlags() {
    return updated ? -1 : 0;
  }

  public Object getValue() {
    return value;
  }

  public void setValue(Object value) {
    updated = true;
    this.value = handleTypeCoercion(type, value);
  }

  private static Object handleTypeCoercion(Class type, Object value) {
    if (type != null && value != null && value.getClass() != type) {
      if (!canConvert(type, value.getClass())) {
        throw new RuntimeException("cannot assign " + value.getClass().getName() + " to type: "
            + type.getName());
      }
      try {
        return convert(value, type);
      }
      catch (Exception e) {
        throw new RuntimeException("cannot convert value of " + value.getClass().getName()
            + " to: " + type.getName());
      }
    }
    return value;
  }

}